Causes and classification of atrial fibrillation
Common causes of atrial fibrillation are hypertension, cardiomyopathy, mitral valve and tricuspid valve disease, hyperthyroidism and increased alcohol consumption. Less common causes: pulmonary embolism, atrial septal defect, congenital heart defects, chronic obstructive pulmonary disease, inflammation of the myocardium and pericardium (pericarditis). Atrial fibrillation is acute when the onset is less than 48 hours.
Paroxysmal atrial fibrillation lasts less than 48 hours and spontaneously is converted to sinus rhythm.
Persistent atrial fibrillation lasts longer than 7 days and for conversion to sinus rhythm require treatment.
Permanent atrial fibrillation can not convert to sinus rhythm. As atrial fibrillation lasts longer, the more less likely to spontaneously convert to sinus rhythm or convert using treatment (because the phenomenon of remodeling).
Symptoms and signs of atrial fibrillation
Often there are no symptoms. Most people blame palpitations, chest discomfort or symptoms of heart failure (feeling of weakness, dizziness, dyspnea – shortness of breath) especially when the heart rate is very high (140-160 beats per minute). Secondary to systemic embolism patients may have symptoms and signs of a stroke. Fibrillation is an irregular heart rate. Pulse deficit means that centrally perceived frequency is higher than that seen in the periphery is often present.
Diagnosis is based on an electrocardiogram. To make an initial evaluation, an echocardiogram and thyroid function tests are needed. Using echocardiography we can identify abnormalities in the structure of the heart: left atrial enlargement, left ventricular kinetic disorders, valve dysfunction or cardiomyopathy. It also can detect factors that increase the risk of stroke like stasis and thrombus formation, the presence of complex aortic plaques. The thrombus is detected best by transesophageal echocardiography.
Atrial Fibrillation Treatment
We need to find the causes of atrial fibrillation, then the treatment should be directed toward control the frequency, rhythm and preventing embolism.
Frequency Control: it must be less than 80 beats per minute at rest to prevent changes due to tachycardia. Beta-blockers (metoprololum) are preferred in cases where it is suspected thyroid disease and atrial fibrillation given by exercises and effort, calcium channel blockers (verapamil) are also indicated. In patients with heart failure is administered digoxin. When these drugs are not effective will introduce amiodarone. In patients who do not respond to drug therapy, radio-frequency ablation of the atrioventricular node is done to achieve a complete block.
Conversion to sinus rhythm in the acute phase is done by synchronous cardioversion or drug preparations. Before converting heart rate should be below 120. If fibrillation lasts more than 48 hours then the patient should receive anticoagulant therapy, if possible anticoagulation should be made at least 3 weeks before conversion and then followed indefinitely because fibrillation can occur again. Drugs used for conversion are antiarrhythmics class IA like procainamide, IC like propafenone or III like amiodarone. ACE inhibitors attenuate myocardial remodeling (which may be the cause of fibrillation in patients with heart failure).
Thromboembolism prevention is made by taking anticoagulants indefinitely. If the patient is healthy and had an episode of atrial fibrillation it will take 4 weeks the anticoagulant therapy. Warfarin anticoagulation is used. If this is contraindicated it can be used aspirin, which is less effective. If there is absolute contraindication to warfarin then the left auricle can be ligated with a surgical procedure or closed by catheterization.